The present invention relates to an apparatus for air drying a granular material in a drying store and for pneumatical emptying of the store, comprising a plurality of air channels extending along a bottom surface of the store and provided with wall openings for the inlet of drying air from the channels into the material and for the outlet of the material from the store through the channels, the channels being connected with means for blowing drying air into the channels and means for providing a flow of conveying air through the channels towards a collector area for the material to be exhausted from the store. Such an apparatus is known from the Danish patent application No. 1878/81. In that apparatus the grain as filled into the drying store onto the bottom channels may be subjected to drying air, which is blown into the channels from one end thereof, while the opposite end is closed by a valve, whereby the air will be forced out into the grain through the wall openings of the channels. Corresponding apparatus were previously known, in which the channels were permanently closed at said opposite end, and in which the air was blown out obliquely forwardly and outwardly through the wall openings, whereby the grain in the bottom layer between the channels was correspondingly affected by a force component forwardly along the channels, i.e. forwardly through the space between each pair of parallel channels. In this latter arrangement the air was usable for conveying the grain out of the store subsequent to the drying of the grain by opening outlet openings located between the channels adjacent their other or closed end and if necessary, also by increasing the air flow. However, considerable dust problems are created in the store in such a system and, moreover, a powerful blower is necessary. In the first described known apparatus, the grain is conveyed out of the store by opening the channel ends, which are closed during the drying, and by making use of guide plates mounted adjacent the channel wall openings so as to project forwardly and inwardly into the channels, whereby the blower air will flow through the channels and thereby, by injector action, suck grain into the channels through the wall openings. The grain will thus be successively drawn into the channels and be let out therethrough, whereby the dust problems are drastically reduced, just as it will be unimportant that during the drying some intrusion of grain will take place into the channels through the wall openings thereof. However, a dust problem still exists to a certain degree, and it is still necessary to utilize a considerable blower capacity for effecting the outlet conveying of the grain.
The present invention is based on the recognition that the outlet conveying of the grain for emptying the store is advantageously effected by way of an active suction from the outlet end of the channels. It has been observed that the bottom mounted channels are thereby able to effectively suck in the grain through the wall openings with the result that the aforementioned dust problem is not only reduced, but really eliminated, and that the necessary power effect for the outlet conveying of the grain is considerably reduced as compared with the known apparatus, without any change of the ability of the apparatus or the channels to introduce drying air into the grain through the wall openings of the channels by means of a suitable blower.
Therefore, it is possible with the invention to utilize one and the same blower for effecting both the blowing in of drying air and the conveying suction, since the blower may be connected with the outlet end of the channels through a suction/blowing switch system, whereby for the blowing in of the drying air it will be unimportant that the air through the channels is supplied with inversed direction relative the known apparatus.
In this connection the invention comprises a special blower unit containing a continually operating blower, which is switchable between blowing and suction operation solely by means of switch valves in a specially designed blower housing.